After bringing it to a boil, could I move it to a slow-cooker for the long simmer? I need to leave the house and i'd rather leave that unattended than a gas burner.
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That should be fine, but you may want to leave it uncovered -- there is a lot of liquid that cooks off during the simmering phase.
I believe you'd have to have the crockpot preheated -- maybe put a quart or so of water in it, leave on a high setting so the water is at least scalded (or pour it in at a boil). Otherwise your temperature will be too low for cooking to continue, and a low temperature might put the sausage at risk of bacterial growth.
Another solution would be to complete cooking while you're home and refrigerate, then reheat later.